backend: Fix enum constructor default parameters

The problem was observed in the follwing code:

enum class A(one: Int, val two: Int = one) ...

The problem is in the `two` default value. Here the enum constructor
lowering used an old (not lowered) symbol for `one`. Also the lowering
didn't copy the default expression for DEFAULT class.
The patch fixes both problems.

backend.native/tests/codegen/function/defaults10.kt

@@ -0,0 +1,7 @@
+enum class A(one: Int, val two: Int = one) {
+    FOO(42)
+}
+
+fun main(args: Array<String>) {
+    println(A.FOO.two)
+}